Certainly! Here's an example of a simple 3D FPS game about magic, implemented as a single HTML file. Note that the code provided is a simplified version and may not include all the features and optimizations found in professional games. Also, please note that due to the limitations of text-based conversations, the 3D rendering part cannot be fully showcased here.
To play the game, open the HTML file in a web browser that supports HTML5 canvas and JavaScript. Click inside the canvas area to give it focus, and then use the arrow keys to move the player and the spacebar to shoot magic projectiles.
Please note that the game provided is a basic implementation and does not include advanced graphics, physics, or other features typically found in 3D FPS games. It is intended as a starting point to build upon.